Electrical systems installed during construction of residential and/or commercial/industrial building require connection of insulated wires which extend between different locations, such as between wall plug-in sockets and circuit breaker panels. Insulated wire may be run in one of several forms of a raceway between electrical devices. This may be a specialized bendable pipe, called a conduit, or one of several varieties of metal (rigid steel or aluminium) or non-metallic polyvinyl chloride (PVC) or high-density polyethylene (HDPE) tubing. Rectangular cross-section metal or PVC wire troughs (North America) or trunking (UK) may be used if many circuits are required. Wires run underground may be run in plastic tubing encased in concrete, but metal elbows may be used at corners of building walls to enable pulling wire around the corners. Wiring in exposed areas, for example factory floors, may be run in cable trays or rectangular raceways having lids.
A problem with electrical construction occurs when PVC conduit is used during structural layout for providing a path for wiring and the conduit is initially placed at corners of building walls, or at a corner between a vertical building wall and the floor, or the ceiling. In most cases, at a later stage after structural layout, electrical wiring installation is performed by an electrician or other construction workers. As shown in prior art FIG. 1a, during the structural layout or at a later stage, an indentation or niche is formed in the wall for initial placement of the PVC conduit. The PVC conduit is shown with a curvature but will not by itself remain with this shape, since it normally rises and reaches an almost straight profile. Therefore, there is a need to retain the curvature for the wire pulling/wire pushing activity associated with wiring installation.
Sometimes the wall niche is provided between support frame elements extending vertically, typically made of metal. A hole is usually formed in the vertical support frame element near the floor at the bottom of the support frame element, for receiving the PVC conduit portion extending from the floor. The PVC conduit upper portion is then placed in the niche, and bent at the corner near the floor, and only later in the construction process is the cable pulled through it.
Typically, the bend or arc of curvature of PVC conduits around the corners of building walls is formed at a tight angle. Sometimes, after having been initially placed at a corner during the structural layout, these conduits are pushed further into the corner during later structural construction by other workmen, such as during flooring installation, plumbing installation, or plasterboard construction. As a result of this pushing, the PVC conduit no longer retains a curvature, and becomes crimped at a sharp angle. There is also the risk of cutting the PVC conduit when it is pushed up against the metal edge in the hole of the support frame element. When the PVC conduit is pushed and crimped or cut as described, it becomes impossible to pull wiring through the PVC conduit around these corners, and also impossible to push wiring ahead through the conduit from an entry point.
Also, there is the risk of an electrical fault if the PVC conduit is cut and the metal frame element comes into contact with the wiring in the conduit.
FIG. 1b (prior art) illustrates this problem at a building corner with a bent PVC conduit. The bent shape restricts the movement of wiring pushed or pulled through it.
Sometimes, cement is poured to seal the PVC conduit at the corner of the wall near the floor, and before the cement dries and becomes hardened, it is necessary to retain the shape of the PVC conduit, by using weights to immobilize it. Here again, the formation of a sharp bend or angle in the PVC conduit causes problems.
Therefore, it would be desirable to provide a solution to the problem of cable conduit crimping and distortion at bends and corners of structural construction.